With development of the communication technique, various types of wireless communication devices such as computers, personal digital assistants, mobile phones, and the like emerge. The wireless communication devices have a function of wireless communication and thus, facilitate transmission of information and data greatly.
A wireless communication device has an antenna to implement the function of wireless communication. In general, the antenna is designed for a typical use mode of the wireless communication device. When the wireless communication device operates in the typical use mode, the antenna has a good working performance, so that the wireless communication device can communicate efficiently.
Nevertheless, it is necessary for the current wireless communication devices to operate in a variety of environments, and the functions of the wireless communication device have been enhanced gradually to possess different use modes. When the wireless communication device changes the use mode thereof and is not within the typical use mode, the working band of the antenna designed for the typical use mode shifts, thus causing the deterioration of the performance of the antenna. Hence, a traditional antenna is not suitable for all of the use states; the performance of the antenna may deteriorate, and the antenna might even malfunction. In addition, when the environment, where the wireless communication device is located, varies, for example, when the wireless communication device is close to the human body or close to an electromagnetic environment, the working band of the antenna can also shift. Therefore, the traditional antenna cannot deal with the effects that result from the variation of the use mode or the environmental condition.
When the working band of the antenna shifts, generally, the working band thereof is broadened to compensate the effect of the frequency shifting due to the variation of the use mode or the environmental condition. However, a great deal of human power and time to adjust the shifted working band is needed, and as the limitations of various techniques, it is difficult to increase the working band of the wireless communication device. Therefore, there are disadvantages to addressing the issue of the frequency shifting by increasing the working band of the antenna, such as high cost, poor effect, and the like. In addition, under a certain environmental condition, for example, in the case that a human body is close to the antenna, the performance of the antenna is often deteriorated artificially to satisfy SAR (Specific Absorption Rate) standard of the electromagnetic radiation to comply with the requirements of a certification test. Hence, the traditional antenna cannot meet the requirements of both the high radiation efficiency and that of the SAR standard.